Definition of "unfavourable"

The shade of a dense pine wood, is more unfavorable to the springing up of pines of the same species than of oaks within it.

1863, Henry David Thoreau, chapter 6, in Excursions

Elizabeth was now most heartily sorry that she had, from the distress of the moment, been led to make Mr. Darcy acquainted with their fears for her sister; for since her marriage would so shortly give the proper termination to the elopement, they might hope to conceal its unfavourable beginning from all those who were not immediately on the spot.

1813 January 27, [Jane Austen], chapter VIII, in Pride and Prejudice: […], volume III, London: […] [George Sidney] for T[homas] Egerton, […], page 148

The fact that the bride went through the ceremony without her bridal bouquet is looked upon by many as an unfavorable omen.

1903, Anna Katharine Green, chapter 6, in The Filigree Ball

[Y]et the thing she most dreaded was to offend the gypsies, by betraying her extremely unfavourable opinion of them, [...]

1860, George Eliot [pseudonym; Mary Ann Evans], “Maggie Tries to Run away from Her Shadow”, in The Mill on the Floss […], volume I, Edinburgh, London: William Blackwood and Sons, book I (Boy and Girl), pages 208–209

The wind was right under the land, the tide unfavorable.

1855, Herman Melville, chapter 17, in Israel Potter